Geez...these negative posts about the 5DMKII's AF with kids has me worried. I currently have an unopened 5DMKII w/ 25-105L F4 kit lens (great price), 70-200L F4 IS, and the 85 1.8 waiting for Christmas. This would be my first DSLR. My current SLR is a film Nikon N90s from the mid-1990s, but it hasn't gotten much use lately as I just don't have time for film anymore. I have never had a problem with its ancient AF.
It seems that old school shooter have much less problem with the AF on the 5DII.
For portraits and when they are not running at 100mph, the AF on the 5DII is more than up to it providing:
- the light is decent
- you use the center point for AF
- use SERVO rather than One Shot
Just for the doubters - here is a panned train on a 5D at 1/25, f11, iso50
brian, no one is doubting the 5d's ability during panning and a portrait setting with subjects posing, etc... (even though you have to use the center point and recompose I think is BS, but to each their own)... but in moving situations, unpredictable situations, kids, even like kids on a merry go round where not only is the positioning changing but depth of field within the scene depending how deep they are within thing... stuff like that can be a bit challenging for this camera... Scenes like that you can always use center point but given how quick everything is, you get in a habit of keeping your subject centralized which takes away from the ability to compose... stuff like that the 7d would have a field day with... The perfect camera in my humble opinion would be the 5d2 image and sensor, 7D or 1d AF, and keep the puppy at the current price point. =)